1. Field of the Invention
The present invention relates to a heating device and a fuser, both using electromagnetic induction, for use in an image forming apparatus of the electrostatic recording type, such as a copying machine, facsimile, and a printer. More particularly, the invention relates to a fuser for fixing a toner image, which is based on electromagnetic induction heating system.
2. Description of the Related Art
Recently, in the image forming apparatus, such as a printer, a copying machine and a facsimile, the market increases demands of energy saving and high speed operation. To meet such market demands, it is important to improve a heating efficiency of the fuser used in the image forming apparatus.
In the image forming apparatus, an unfixed toner image is formed on a recording material, such as recording sheet, printing paper, or electrostatic recording paper, by an image forming process by, for example, xerographic, electrostatic or magnetic recording, and by an image transfer method or a direct method. Examples of widely used fusers for fusing and fixing the unfixed toner images are the fusers of the heating roller type, the film heating type, and the electromagnetic induction heating type.
A fuser of the electromagnetic induction heating type is disclosed in Japanese Unexamined Patent Publication No. H08-22206. In the fuser, eddy current is caused in a magnetic metal member by an alternating magnetic field applied thereto, Joule heat is generated therein by the eddy current, and the heating member including the metal member is induction heated.
The fuser of the electromagnetic induction type is such that a magnetic field is developed by an exciting coil, and eddy current is caused in the surface region of the conductive roller by the magnetic field. The support frame made of resin or the like, located near the conductive roller, is subjected to high temperature. Accordingly, when it experiences a long time use, it is disadvantageously warped.
Further, there is such a problem that noise is generated in members or devices located near the fuser, by unnecessary radiation by leaking magnetic fluxes caused by the exciting coil.
Furthermore, since high voltage is applied to the exciting coil, a housing is provided at the opposite side of the heating member of the induction heating unit to prevent an electric shock. Since the exciting coil etc. located near the heating member is subjected to high temperature, resin material of a flame resisting grade is used for the housing. However, according this structure, the temperature in the induction heating rises, and enamel coated on a wire of the exciting coil melts, and it may cause a short or leak, hence a reliability of fuser is decreased.